Many free software activists are also active for good causes in other areas than software. The non-evil clause costs them time and nerves and distracts them from doing good.
Douglas Crockford uses the MIT free software license with the additional clause:
"The Software shall be used for Good, not Evil."
This clause makes his software effectively non-free because there is no universally accepted definition of good and evil: https://en.wikipedia.org/wiki/Good_and_evil
More details: https://wiki.debian.org/qa.debian.org/jsonevil
Please explain to Crockford, why his reasoning for the license is wrong.